DE3138980A1 - Directional coupler for optical signals serving as a switch - Google Patents

Abstract

Directional coupler for optical signals serving as a switch and made using integrated technology, two closely adjacent light guides (A-A', B-B') which are arranged in parallel along a coupling section being mounted on a substrate, e.g. of LiNbO3 by means of Ti doping, and electrically controllable electrically conductive electrodes (E11...E24) being respectively mounted on the light guides along the coupling section, which electrodes pass on the light guided in the relevant light guide (A-A') directly (from A to A') or exchanged crosswise (from A to B') between the light guides, depending on the electrical control voltage (V1-V2) between the electrodes. The level of the control voltage can be reduced owing to the fact that at least two electrodes (E11...E14, E21...E24) are mounted in each case one behind another along the coupling section on both light guides in such a way that in each case one electrode (E11) on the first light guide (A-A') is situated opposite an electrode (E21) on the second light guide (B-B'), and that the two opposite electrodes (E11/E21, E12/E22,...), which form an electrode pair in each case, can be controlled separately by in each case another potential (V1 at E11, V2 at E21) of the control voltage (V1/V2). Furthermore, each electrode (E11) on the first light guide (A-A') is connected in an electrically conductive fashion in each case to an electrode (E22) on the second light guide (B-B'), which electrode (E22) belongs to another, preferably adjacent, electrode pair (E12/E22). <IMAGE>

Description

Directional coupler used as a switch for optical signals

The invention relates to a special switch for optical signals in integrated technology, especially for a switching network with purely optical Intermediate lines in a telephone switching system.

In addition, however, the invention is also suitable for others Cases in which light should be switched in a light guide.

The invention is based on a special directional coupler, compare the preamble of claim 1, which for itself e.g. by Electronics Letters 12 (October 28, 1976) No 22, 575 - 577, in particular Fig. 2 on page 576, as well as Appl. Phys. Lett. 28 (1st Maf 1976) No. 9, 503-506, particularly Fig. 1 (a) Page 504, is previously known. In these known directional couplers are each along the coupling path of one of the two light guides, the first light guide, one behind the other two separately controllable electrodes attached, but on the other, second light guide only one very long electrode at a time, in such a way that each of the two electrodes on the first light guide opposite the single electrode of the second light guide, based on the longitudinal direction of the coupling path.

These known directional couplers already require significantly less Control voltage between the electrodes, to reliably use this as To switch through the directional coupler serving either directly or crosswise, compared to the known directional couplers, which only have a single electrode is attached to each light guide per coupling path.

The object of the invention is the control voltage between the electrodes to be able to further reduce the directional coupler considerably.

This object of the invention is achieved by the characterizing part of the claim 1 resolved.

The additional measure mentioned in claim 2 allows the relevant control voltage or the relevant control voltages continue to be significant to be able to reduce.

The invention is explained in more detail with reference to the two figures.

Figure 1 shows a particularly simple example of the invention with two Electrodes along each light guide within the coupling path. With the in Fig.2 The example shown are four electrodes per light guide within the same coupling path appropriate.

In both figures, there is one as a switch Serving directional coupler for optical signals in integrated technology. There are each closely spaced, e.g. at a distance of 3, along the coupling path Light guides A-A ', B-B' attached to a substrate. With the substrate it can be E.g. LiNb03, which was e.g. doped with Ti, to the light guide to produce in the substrate.

In principle, however, the invention is not directed to a substrate this material is limited because of the physical effect that is used in the hallmark of claim 1 is based on the measure specified, in principle also with substrates can be achieved from other materials.

Both figures are examples of those on the light guides electrically controllable, electrically conductive electrodes along the coupling path E11..22 or 0Ei1. .E24 are attached. These electrodes allow, depending on the electrical control voltage, compare V1 / V2, between the individual electrodes, to forward the light supplied in one or in both light guides directly or exchanged crosswise between the light guides. With the direct The light supplied at A is passed on via the first light guide at A ' and the light supplied to the second light guide via B is carried away at B '. In contrast, if the forwarding is crossed, this becomes the first light guide at A Supplied light at B 'dissipated via the second light guide and that at B the second light guide supplied light via A ', that is dissipated via the first light guide. Such switches have also been used for electrical instead of optical signals since Known for a long time, especially in connection with the formation of more complicated Switching networks of telephone switching systems, compare DE-AS 20 36 176 and 20 36 128, as well as US 3,593,295 and 3,638,193.

In the illustrated embodiments of the invention are along the Coupling path on both light guides, and not just on one of the same, one behind the other at least two electrodes attached.

These electrodes are attached in a special way so that) namely one electrode at a time, compare E11, on the first light guide A-A 'is opposite an electrode, compare E21, on the second light guide B-B'. In addition, the two electrodes, each opposite one another, are to be compared E11 / E21 and E12 / E22, separately controllable. These opposing electrodes, compare E11 / E21, so each form a pair of electrodes in which each of the Both electrodes are each controlled by a different potential of the control voltage V1 / V2 will. Note in particular in the figures that the electrode E11 from.

Potential VI, but the opposite electrode E21 at potential V2 of this control voltage is controlled.

Despite this large number of electrodes in the invention - it contains namely at least 4 electrodes per coupling path, but it is not absolutely necessary at least three potentials to control the switch and beLm.Standß the EechnIk. za use "vIt turned out that the control as a switch is sufficient is that each electrode, compare Ell, on the first light guide A-A 'is electrical conductive with an electrode belonging to another pair of electrodes, compare E22, is connected to the second light guide B-B '. With those shown in both figures In the simplest case, examples are only two different potentials, compare V1 and V2, to control all electrodes based on such crosswise conductive Connections between the electrodes are necessary, with insulating layers being short-circuited between V1 ß 2 obstructing O Wel in the invention not only on one light guide, but several electrodes of their own are attached to each of the two light guides, which, seen in the longitudinal direction of the coupling section, alternately one behind the other can be controlled with different potentials is the level of the control voltage V1 / V2, which are necessary for switching in both switching states, clearly in each case smaller than if only a single, very long electrode on one of the two light guides would have been attached.

In addition, it was shown that the influence on the speed of light of the light rays in the two light guides along this coupling path, respectively the more intense it is, the more electrodes in a row on each of the two light guides Particularly low levels of the control voltage are, see Fig. 2, achievable if more than two pairs of electrodes are attached along the coupling path - in the example shown in Fig. 2, four pairs of electrodes are attached.

In principle, the control voltage can be further reduced as a result, that more than four pairs of electrodes along the coupling path of this directional coupler be attached.

Accordingly, the invention makes use of the fact that the speed of light.in the light guides are particularly strongly influenced by particularly rapid changes, i.e. especially short lengths of the electric fields, generated by means of special many electrodes per light guide - despite a reduction in control voltages, even if the length of the coupling path is not changed. One can indeed by that if the coupling distance is extended, the levels of the control voltages are also reduced. With the invention, however, it is possible alone without extending the coupling path by increasing the number of electrodes along this coupling path, i.e. through Reducing the size of the electrodes, reducing the control voltage. With the in Fig.

1 and 2, the coupling path has e.g. 3mm in length, the electrodes in Fig. 1 approx. 1.5 mm, in Fig. 2 approx. 0.7 mm in length exhibit. Because of the low control voltages, the invention can even often a shortening of the length of the coupling path, i.e. a reduction in the space required on the substrate.

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Claims (2)

~ Patent claims 1. Directional coupler serving as a switch for optical Signals in integrated technology - two closely spaced along a coupling path Light guides (A-A ', B-B') arranged in parallel on a substrate, e.g. made of LiNbO3 by means of Ti doping, are attached, - on the light guides along the coupling path In each case electrically controllable electrically conductive electrodes (Ell ... E24) attached are which, dependent. of the electrical control voltage (V1-V2) between the Electrodes, the light guided in the respective light guide (A-A ') directly (from A to A ') or interchanged between the light guides (from A to B '), especially for a switching network with purely optical intermediate lines in a telephone switching system, characterized in that - along the Coupling path on both optical fibers, one behind the other, at least two electrodes each (E11 ... E14, E21 ... E24) are attached in such a way that X --- one electrode (Ell) each on the first light guide (A-A ') opposite an electrode (E21) on the second light guide both opposite electrodes (Ell / E21, E12 / E22, ...), each with a Form a pair of electrodes, separated from each other by a different potential (V1 on Eil, but V2 at E21) of the control voltage (V1 / V2) can be controlled, and - each electrode (a) on the first light guide (A-A ') each electrically conductive with one to one other, preferably adjacent electrode pair (E12 / E22) belonging electrode (E22) is connected to the second light guide (B-B '). 2. Directional coupler according to claim 1, characterized in that that - more than two pairs of electrodes are attached along the coupling path.